Several years ago I typed up a rough English translation of André Joyal’s hard-to-find 1977 paper Remarques sur la théorie des jeux à deux personnes, describing the category of Conway games.
My version was on the web server of the University of Manchester mathematics department for a while: I’ve just noticed that it’s not there any more, which is understandable. I’ll put a copy here, in case it’s useful to somebody.
added on 2010-12-29: I’ve updated the file with a version that includes a correction to the definition of the sum of games. Thanks to Glynn in the comments (presumably Glynn Winskel?) for reminding me of this error. Apologies for mistakenly uploading the uncorrected version.